1. Field of the Invention
This invention relates to television receivers, in general, and to a high frequency de-peaking circuit for the video amplifier output stages thereof, in particular.
2. Description of the Prior Art
The use of video peaking circuits in television receivers to accentuate the high video frequencies is well known in the prior art. Typical of such circuits are those disclosed in U.S. Pat. Nos. 3,320,361 -- Stroh, 3,340,357 -- Williams and 3,394,319 -- Heuer. Each of these patents points out the further desirability of providing an adjustable control in the peaking circuit to allow the viewer to vary the band-pass receiver characteristic so as to optimize the reproduced picture in the presence of weak signals. Since the signal-to-noise ratio may be sufficiently poor under such signal conditions as to introduce "snow" into the image, adjustment of the control to de-emphasize the accentuated higher video frequencies of the signal is employed to "smear" the noise, as most of its components are at those higher frequencies. When the signal transmissions are good, however, the control is adjusted to translate the accentuated high-frequency video content intact, so that the high quality signal may preferably be reproduced in its full detail. While it has been recognized that such picture optimization can be had to some extent through adjustment of the receiver's fine tuning control (see U.S. Pat. No. 3,487,165 -- Anderson), it is now recognized that such de-tuning may result in the loss of color information during color reception--and may change the sound reproduction of the receiver, as well.
With the advent of such color television transmission and receiving systems as are capable of presenting an extremely high resolution color display, this problem of increasing visibility of video noise becomes more significant. Thus, as noted in these patent disclosures, television set manufacturers have provided the viewer with manually operated "sharpness" or "crispness" controls to permit an adjustment to be made in the video frequency response as will produce a more pleasing image in accordance with his individual taste.
However, characteristic of each of these controls is the need for the viewer to continually re-adjust its setting each time he changes the channel selector, else the visual presentations will not be optimum for each channel to which he tunes. This follows from signal variations which occur with different studio operations, with different transmitter adjustments, with over-the-air transmission paths which differ, and with differences in the quality of the televised information--for example, old movies as compared to live performances. Besides being thus disadvantageous from the standpoint of requiring the viewer to continuously re-adjust his sharpness control to maintain an optimum picture, such approaches are disadvantageous in that the viewer will many times forget to reset the control and will, therefore, lose the performance which just such a control is intended to provide. Perhaps more important is the fact that this arrangement provides the viewer with a control whose function he may not fully appreciate, and is in a direction away from the goal of having as many adjustments done automatically, in order to simplify matters for the purchasing customer.